1. Field of the Invention
The invention relates to a method of treating swimming pool water which includes chlorination of the swimming-pool water and filtration of the swimming-pool water via a fixed-bed filter, with periodic backflushing of the filter with wash water to which a disinfectant is added. The backflushing process of the invention results in a distinctly improved quality of the swimming-pool water, less contamination of the drained-off wash water with harmful substances and reduced need for addition of chlorine.
2. Background Information
In order to maintain the quality of swimming-pool water, it must be purified in a continuous preparation system in order to comply with hygienic requirements. The method for treating swimming-pool water comprises filtration of the swimming-pool water via a fixed-bed filter, which can be designed as an open or closed filter, especially as a single-bed filter, two-bed filter or mixed-bed filter. Substances which are colloidally present and a portion of the truly dissolved substances are converted into a state which can be retained in the filter with the aid of a coagulant added to the pool water in the infeed of the filter. A portion of the genuinely dissolved substances can be coagulated by chemical sorption. Microorganisms are also retained in the separating precipitate and in the pores of the filter material. Since such microorganisms can multiply in the filter it is required that the filter must be periodically backflushed with the greatest possible efficiency. Normally, coagulants from the series polyaluminum chloride, aluminum sulfate, sodium aluminate, iron-III-chloride and copper sulfate are added to the swimming-pool water before its passage through the filter. The filtrate exiting from the filter passes back into the swimming pool.
Because of the constant discharge of germs by bathers into the swimming-pool water, the treatment of swimming-pool water must also include effective disinfection. This is normally accomplished by chlorination such as is documented in DIN 19643, optionally in combination with an ozonization. Current chlorination methods are the hypochlorous-acid method, the chlorine/bleaching-solution method and the chlorine-chlorodioxide method. The chlorination advantageously takes place in the previously mentioned filtrate.
In order to discharge the floccule separated in the filter and the slime forming because of the organic matter, and to avoid an uncontrolled multiplication of microorganisms in these flocs as well as in the pores of the filter material, special emphasis is given to the backflushing process using wash water removed from the circulation. The effectiveness of the backflushing process considerably determines the quality of the filtrate. In many instances the clogging material is removed from the filters only by the physical action of the water. However, such purification is incomplete because slimy precipitation products as well as biomass remain permanently adhered to the filter material. Thus, there is the risk that microorganisms which are often infectious will multiply considerably and be carried into the pool water with the filtrate. In order to prevent or at least reduce the risk of a contamination of the filter with critical microorganisms such as Legionella pneumophila or Pseudomonas aeruginosa or fecal coliform bacteria an additional disinfection is necessary. In the known filter disinfection with chlorine, the wash water is compounded with chlorine (approximately 10 mg/l) after one or several wash phases and after an exposure time the wash water is removed into a water storage or into a conduit. The use of chlorine in filter disinfection has a number of disadvantages: Chlorine does have an excellent germicidal action; however, slime and algae are insufficiently separated from the surface of the filter material, so that microorganisms continue to be hidden. A further significant disadvantage can be seen in the fact that organohalogen compounds are formed by the interaction of chlorine with organic substances, which increases the content of undesirable AOX substances (adsorbable organic halogens). In addition, when such wash water is discharged into the sewage system, the breakdown action in biological clarification stages of a sewage treatment plant can be diminished, also by the high residual amounts of chlorine compounds which continue to be active.
The use of ozone rather than chlorine as disinfectant in filter backflushing is also known. Ozone has, like chlorine, a very good microbiocidal action; however, significant investment costs are required for the installation of an ozonization system as well as for the additional corrosion protection and safety devices.
Note concerning the general state of the art the monograph "Aufbereitung von Schwimmbadwasser" [German=Preparation of Water for a Swimming Pool], Wilhelm Herschman, Krammer-Verlag, 1980. Chapter 2.1 treats coagulative filtration (pages 34-41), chapter 2.9 the filter materials and auxiliary chemicals (pages 61-64) and chapter 3 the disinfection of bath water. DIN 19643 also teaches the preparation of swimming-pool water.